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1、环境科学专业英语-第二节Unit2:PopulationResourcesandEnvironmentAlltoooften,overpopulationisthoughtofsimplyascrowding:toomanypeopleinagivenarea,toohighapopulationdensity.Between1900andnow,theworld'spopulationhasroughlyquadrupledfromabout1.6billionin1900toabout6billiontodayandiscurrentlygrowin
2、gatanannualrateof1.2%,or77millionpeopleperyear.Sixcountriesaccountforhalfofthisannualgrowth:Indiafor21%,Chinafor12%,Pakistanfor5%,Nigeriafor4%,Bangladeshfor4%,andIndonesiafor3%.By2050,worldpopulationisexpectedtobebetween7.9billion(lowvariant)and10.9billion(highvariant),withthemed
3、iumvariantproducing9.3billion.Therewouldbearapidagingoftheworld'spopulation.Inthepast,themedianagefortheworld'spopulationhasbeenbetween20and25years.Itisnowabout26years.By2050,themedianageforadepopulatingglobewouldbeabout42years.Inthemoredevelopedregionsthemedianageofpopulationwou
4、ldbeover50.Thatistosay:foreverypersonundertheageof50,therewouldbesomeoneovertheageof50.Acompletetransformationoftheprofileoftheworldwouldthusoccur.Theexplosionofworldpopulationisanoutgrowthoftheindustrialage,andthreekeyfactorsaretoblame:increasedfoodproduction,diseasecontrol,andb
5、ettersanitation.Theseadvancesgreatlyincreasethesurvivalrateofnewborns,butthisgreatchangeoccursinmanycountrieswithoutanydecreaseinthenumberofbirths.Populationgrowthisattherootofvirtuallyallenvironmentproblems,includingpollutionandresourcesdepletion,andindirectsocialdisruptions,suc
6、hashousing4环境科学专业英语-第二节shortages,malnutritionandinadequatehealthcare.Rapidgrowthinpopulationcreatesdifficultiesinmeetingthebasicneedsofpeople,whilecrowdingmaycausementalillness,drugabuseandvariousformsofantisocialbehavior.Hunger,starvation,disease,poverty,illiteracy,pollution,une
7、mployment,andbarrenlandscapesare,tomanyobservers,signsthatthehumanpopulationismuchtoobigfortheearth'sresources.Amongthenegativetrendstheybetwouldcontinueare:risingglobaltemperature,shrinkingamountofcroplandperperson,declineinamountofwheatandricegrownperperson,shrinkingareaoftropi
8、calmoistforests,decreasingoceanicfishhar
